1. Field of the Invention
The invention relates to an image forming apparatus such as copying apparatus, electrophotographic printer, or the like and, more particularly, to the improvement of a driving system of a photosensitive drum equipped for such an apparatus.
2. Related Background Art
Hitherto, a color image forming apparatus such as copying apparatus, electrophotographic printer, or the like for performing color printing of yellow (Y), magenta (M), cyan (C), and black (K) has been known. The following system is used as a representative system for such a color image forming apparatus.
(1) A tandem system in which four independent light sources and image drum units (hereinafter, referred to as “ID units”) serving as image forming processes are arranged in the conveying direction of a print sheet, the conveying direction is set to a predetermined direction, the sheet is allowed to pass, and images of four colors are sequentially printed by the ID units (refer to JP-A-2000-238374).
(2) An intermediate transfer member system in which after toner images of four colors are temporarily formed onto a drum- or belt-shaped intermediate transfer member, they are transferred onto the sheet.
(3) A batch multiple developing system in which, after the toner images of four colors are directly sequentially developed on a photosensitive drum, they are transferred onto the sheet in a lump.
(4) A transfer drum system in which the sheet is wound around a transfer drum and the toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are sequentially directly multiple transferred onto the sheet.
Among them, according to the tandem system, since the color printing can be performed by one processing step, the tandem system has such an advantage that it is suitable for realization of a high speed upon full color printing as compared with other systems. In the tandem system, a DC brushless motor which can rotate at a high speed is used as a driving source for rotating the photosensitive drum. In the DC brushless motor, when a phase current is switched, a spike-shaped current noise occurs. In the tandem system, four ID units are ordinarily arranged. Therefore, there is also a case where the spike-shaped current noises occurring in a plurality of DC brushless motors are multiplexed at same timing and become a large power noise. It is also presumed that such a large power noise causes an unexpected problem in which it induces the erroneous operation of a CPU in the apparatus, it becomes an electromagnetic noise and is dispersed to peripheral equipment, or the like.
It is a problem to be solved that, as mentioned above, if the DC brushless motors are used in the image forming apparatus, when the phase current is switched, the spike-shaped current noises occur, and the case where the spike-shaped current noises are multiplexed at the same timing and become the large power noise can occur.